1. Field of the Invention
The present invention relates to a diagnostic apparatus for an engine, and more particularly to a diagnostic apparatus for examining for possible malfunction in a control to reduce emissions during an engine cold state.
2. Description of the Related Art
Exhaust gas discharged from an automotive engine includes pollutants, such as NOx (nitrogen oxides), CO (carbon monoxide), and HC (hydrocarbon). In order to purify these pollutants, the engine is generally equipped with a catalyst converter including an exhaust-gas purification catalyst such as a three-way catalyst and a NOx absorbing catalyst disposed in the engine exhaust-gas passage. The exhaust-gas purification catalyst, however, provides insufficient purification of the exhaust-gas until the activation temperature has been reached. To cope with this, during engine cold start when the exhaust-gas purification catalyst is still inactive, it is necessary that the temperature of the exhaust-gas purification catalyst be quickly raised, i.e., or the catalyst should be quickly warmed.
Thus, the general automotive engine, during engine cold start, implements a strategy for reducing emission in a cold state, (a logic for reducing emission in a cold state), which corrects a plurality of control parameters for the engine, such as an ignition timing, engine rotational speed (corresponding to the amount of intake-air), or air-fuel ratio (corresponding to the amount of fuel supply) to promote the activation or light-off of the exhaust-gas purification catalyst for enhancing its emission performance. The cold-state emission-reducing strategy is carried out by use of a mechanism, referred to as xe2x80x9ca cold-state emission-reducing mechanismxe2x80x9d, comprising sensors including a coolant temperature sensor, controllable devices including an ignition coil and fuel injector, a control unit for controlling these devices, and other devices. By way of example, a target rotational speed and a target ignition timing (or the amount of ignition retard) of the engine may be set based upon a coolant temperature detected by the coolant temperature sensor in cold start, and then the fuel injector and the ignition coil may be controlled so as to achieve the rotational speed and the ignition timing.
However, in some cases, a malfunction may possibly occur in the sensors, controllable devices, and control unit installed in the engine. Such malfunction will prevent a normal implementation of the cold-state emission-reducing strategy, which impairs the emission performance during engine cold start. In order to detect such a malfunction during the cold-state emission-reducing strategy, an approach has been known which monitors each of the parameters associated with an implementation of the cold-state emission-reducing strategy, such as the amount of fuel injection, ignition timing, and engine rotational speed, as disclosed in Japanese Unexamined Patent Publication No. H08-093564 (U.S. Pat. No. 5,632,250). However, in the case of the respective monitoring of each parameter as above, the eventual deterioration level in emission performance is difficult to recognize. Moreover, the approach inevitably requires the monitoring of a variety of parameters and a complicated calculation of these parameters, which significantly complicates the diagnostic mechanism.
With regard to malfunction detection, the present invention identifies a correlation between the eventual deterioration level in emission performance and the cumulative amount of fuel injection from engine start.
In view of the problem above, an object of the present invention is to provide a simple and easy approach to diagnosis of the cold-state emission-reducing strategy which corrects a plurality of engine control parameters to promote the activation or light-off of the exhaust-gas purification catalyst for enhancing emission performance using the correlation identified by the present invention.
According to the present invention there is provided a diagnostic apparatus for an engine comprising: a catalyst temperature detecting device; a catalyst warming device; a cumulative fuel consumption calculating device; and a failure judging device. The catalyst temperature detecting device detects a value associated with the temperature of an exhaust-gas purification catalyst disposed in an exhaust system of the engine. The catalyst warming device corrects a plurality of control parameters for the engine so as to activate the exhaust-gas purification catalyst, when the exhaust-gas purification catalyst is determined to be inactivated based on the detection of the catalyst temperature detecting device. The cumulative fuel consumption calculating device calculates a value associated with the cumulative fuel consumption during a time period after engine start until the elapse of a cumulating period. The failure judging device judges that the catalyst warming device is faulty, when the cumulative fuel consumption is judged to be equal to or less than a judgement threshold based on the calculation of the cumulative fuel consumption calculating device.
The diagnostic apparatus for an engine monitors the cumulative fuel consumption during the period after engine start until the exhaust-gas purification catalyst is activated and determines that the cold-state emission-reducing strategy is faulty if the cumulative fuel consumption is equal to or less than the determination threshold.
Accordingly, the abnormality of the cold-state emission-reducing strategy is accurately and easily detected by merely calculating the cumulative amount of the fuel consumption determined from the cumulative amount of the injection pulse width for the injector (or fuel injection valve) or the cumulative amount of the fuel flow during a cumulating period after engine start, and comparing the calculated cumulative amount with the judgement threshold without monitoring a variety of control parameters for the cold-state emission-reducing strategy.
Preferably, the failure judging device makes a judgement of a faulty condition only during the idling of the engine, because little fluctuation in fuel consumption during idling improves the accuracy of the diagnosis.
In the above diagnostic apparatus, if the catalyst warming device sets a target engine rotational speed and a target ignition timing on the basis of a predetermined characteristic in accordance with an engine coolant temperature during engine start, and adjusts the amount of fuel injection and the ignition timing so as to achieve the target rotational speed and the target ignition timing, the judgement threshold may be preferably set based on the engine coolant temperature at engine start. Alternatively, the judgement threshold may be determined (or estimated) based on a target rotational speed and a target ignition timing, while the cumulating period is fixed to a constant value.
Additionally, in the diagnostic apparatus of the present invention, the cumulative period may be shorter for a lower engine coolant temperature at engine start, while the judgement threshold is fixed to a constant value, rather than correcting the judgement threshold in accordance with the engine coolant temperature as described above.
Other features, aspects, and advantages of the present invention will become apparent from the following description of the invention which refer to the accompanying drawings.